This is a non-randomized, prospective study to evaluate the progression of bone loss in patients with primary hyperparathyroidism. The hypotheses to be tested are: 1)Bone loss in untreated patients is progressive over time; 2)Treatment of patients with parathyroid surgery may result in an increase in bone mineral content; 3)Biochemical indices of bone turnover and calciotropic hormones may predict the patients to benefit most from surgery.